SANGER AND BLACK. — QUANTITATIVE DETERMINATION OF ARSENIC. 315 



gen sulphide, with a reduction of thirty minutes' duration. Each set of 

 four was then treated with various reagents and the effects compared. 



Initial Band. The arsenic band appears in a few minutes and is 

 nearly complete before the others begin to form. The deposit is char- 

 acteristic and unmistakable. The phosphorus and sulphur bands are 

 a uniform pale yellow, rather difficult to distinguish from each other. 

 The antimony band is a faint gray. 



Exposure to Air. On standing over night in rather moist, warm 

 air, the arsenic band was slightly bleached, the others unchanged. On 

 lunger exposure the phosphorus band was turned slightly brown on 

 the upper side, and the sulphur band became slightly dark on the 

 upper edge. Heating to 1UJ° had no additional effect on any of the 

 bands. 



Cold Water. The initial set was placed in cold water. After fifteen 

 minutes the antimony band was bleached completely, the phosphorus 

 became paler, while the arsenic and sulphur were unchanged. After 

 fourteen hours the arsenic was considerably bleached, but was still orange 

 red, while the phosphorus had become a very faint yellow and the sul- 

 phur was unchanged. 



Hot Water. The set was boiled with water for one minute. The 

 arsenic and antimony bands wore changed to a grayish white, the 

 phosphorus was bleached to a faint yellow, while the sulphur was 

 unchanged. On standing, the sulphur band became light brown. 



Hydrochloric Acid. The set was warmed to G0° with hydrochloric 

 acid ((> N) for one minute and thoroughly washed. The arsenic band 

 was lengthened and became the usual brilliant red. The antimony 

 was turned slightly gray. The phosphorus became a brilliant lemon 

 yellow, and the sulphur was also brightened, but not so strikingly. 

 On drying, the colors became duller, and on the upper end of the 

 sulphur band was a fringe of dark gray. 



Auric Chloiide. The dried set from the last treatment was im- 

 mersed in auric chloride (n/100) for five minutes. The arsenic band 

 became at once a brilliant purple ; the antimony changed more slowly. 

 The phosphorus slowly turned a characteristic red brown, then to pur- 

 ple, and the final colors of these three bands differed chiefly in inten- 

 sity. The sulphur band had only a slight brownish tinge. 



Ammonia. The set was placed in normal ammonic hydroxide for 

 five minutes. The arsenic band became at once a brilliant black ; the 

 antimony also quickby, but the band was longer and duller in shade. 

 The phosphorus turned slowly black and was not equal finally to the 

 other two in intensity. The sulphur band was not blackened, but 

 changed slightly to a pale brown, somewhat darker on dryim 



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